1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to a block Time Domain Equalizer (TDE) for a Time Reversal-Space Time Block Code (TR-STBC) system, and encoding and equalizing a received signal in the block TDE. More particularly, methods and apparatuses consistent with the present invention relate to the block TDE which has a tap length independent of a data block length and includes training and data blocks in the same block by using a block equalizer where a decoder and an equalizer are combined, so that it can be used in fast time-varying channels, and encoding and equalizing a received signal in the block TDE.
2. Description of Related Art
In the last decade, a huge growth in wireless technologies like cellular telephony, personal/portable devices and the mobile Internet has been seen. The fundamental phenomenon which makes reliable wireless transmission difficult is time-varying multipath fading of the wireless channel. However, recent research has proven that spatial diversity techniques are effective at mitigating this multipath fading.
A Time Reversal-Space Time Block Coding (TR-STBC) scheme in which the spatial diversity technique is adopted combines time-domain filtering, conjugation, and time-reversal operations. Outputs of the TR-STBC decoder are decoupled but contain residual Inter-Symbol Interference (ISI) which must be mitigated using equalizers. FIG. 1 illustrates a structure of a conventional TR-STBC system. As illustrated in FIG. 1, a TR-STBC encoder 101 transmits signals to a TR-STBC decoder 103 from two antennas 102 for the spatial diversity, and the TR-STBC decoder 103 receives, decodes, and then equalizes the transmitted signals using an equalizer 104, thereby obtaining outputs.
Unfortunately, to perform this equalization, the optimal maximum likelihood sequence estimation techniques have exponentially increasing complexity with the signal constellation size and Channel Impulse Response (CIR) length.
Conventional block STBC structures for frequency selective fading channels which have been attempted to solve the above-mentioned problem require explicit knowledge of the CIR with respect to the decoding and equalization of the STBC transmissions. FIG. 2 illustrates a structure of a conventional TR-STBC system in which a block Frequency Domain Equalizer (FDE) is adapted. The TR-STBC encoder 201 transmits signals to a block FDE 202 from two antennas for spatial diversity, and the block FDE 202 decodes and equalizes the transmitted signals. In the TR-STBC system using the block FDE 202 processed in a frequency domain, the CIR is estimated using training sequences or pilot tones embedded in the transmission. Then, the optimum decoder/equalizer settings are computed based on this estimated CIR.
However, as a combined decoder/adaptive equalizer scheme is based on frequency domain block equalization, the equalizer is constrained to have the same length as the data block length. Since combining the training block and the data block within the same block is difficult, there is difficulty in using a conventional TR-STBC system in the fast time-varying channel.